Polarized epithelial cells are a dramatic example of the importance of the organized transport of cellular components. These cells must interact with two distinct environments, one on their apical surface and one on their basal/lateral surfaces. Previous work in the Goldenring lab has shown that the complex of the small GTPase Rab11a and the unconventional molecular motor myosin Vb are important in the apical transport of plasma membrane recycling vesicles in polarized epithelial cells. A combination of specific and random mutational analysis complemented by yeast two-hybrid screening will be utilized in order to determine the structural basis of the interaction between myosin Vb and its binding partners Rab11a and Rab11-FIP2. Additionaly, the components of the endogenous myosin Vb motor complex will be isolated from human gastric parietal cells by immunoprecipitaion of the motor from H/K-ATPase-enriched tubulovesicles, and the identities of the members of the complex will be determined by mass spectroscopy. Results from this work will aid in discovering the mechanisms of regulation of myosin Vb, which in turn will advance our understanding of the general mechanisms of membrane recycling in polarized cells.